I would create a global variable to store the name of the layout that they are leaving, (basically the "From" layout).
Now, when you did your button setup to navigate to the "to" layout, did you trigger a script or just a go to layout command?
Because you would need to create a script now to first store the "from" layout's name in the global field and then navigate to the "to" layout. Then you could add a "Back" button to the "to" layout that would trigger a script to send you back to the "from" layout by getting its name from the global field.
Someone else might have a better idea, but i'm pretty sure this would work.